1. Field of the Invention
The present invention relates to a golf club head having a hollow outer shell made of light metals such as titanium or titanium alloy.
2. Related Art
Traditionally a wood club head has been made of a single persimmon block because it is light in weight and has relatively high strength. However, metals are becoming popular as a material for a golf club head instead of wood because it became difficult to find a suitable wood material such as good persimmon and manufacture costs of such wood material became high. Particularly, in recent years, in order to make the sweet area of the golf club head wider, a hollow shell formed of light metals, such as titanium or titanium alloy, are mainly employed as materials for manufacturing a golf club head.
As the volume of the golf club head made of titanium or titanium alloy is increased, the center of gravity of the golf club head begins to take a higher position, which is undesirable from the viewpoint of smooth swing of the golf club.
In order to lower the center of gravity of the golf club head, a typical golf club head made of titanium or titanium alloy includes at least one insert made of tungsten, whose specific gravity is greater than that of titanium, as a balance weight member. The balance weight member is integrally provided at substantially a middle portion of a sole plate of the club head by bonding, screwing or welding to increase a moment of inertia of the club head by lowering a center thereof.
However, it has been difficult to maintain enough bonding strength between the balance weight member and the sole plate by bonding agent only. Even when they are welded, sufficient welding strength cannot be obtained because the sole plate made of titanium and the balance weight member made of tungsten are different metals and their weldability was not sufficient. Further, when it is intended to connect them by screws, preparation of threads in the parts and assembly thereof are very cumbersome.